This invention relates to an impact printer head for use in printing a dot or dots on a recording medium so that a combination of the dots may represent letters.
In the copending U.S. patent application Ser. No. 381,479 filed on May 24, 1982, by Izumu Fukui et al., a printer unit is proposed which comprises a longitudinal-effect electroexpansive transducer, a printing rod or wire, and a frame member coupled to the transducer and the printing wire for actuating the printing wire towards and away from a recording medium in compliance with expansion of the transducer to print a dot on the recording medium when the transducer is energized or expanded. The longitudinal-effect electroexpansive transducer gives rise to a large displacement as compared with a transverse-effect electroexpansive transducer. This means that the proposed printer unit can save electric power and becomes compact in comparison with a printer unit comprising the transverse-effect electroexpansive transducer.
In order to construct an impact printer head, a plurality of printer units as mentioned above are stacked in a direction of a thickness of each printer unit in parallel to one another to dispose the respective printing wires in parallel. It is mentioned here that each of the printer units is thicker in thickness than each printing wire and that a dot distance between two adjacent dots is preferably as short as possible in order to raise a density of dots in such an impact printer head. This enables a letter to be printed with a greater number of dots to make a letter appear more clearly as compared with the letter printed with a less number of dots.
Since the dot distance is dependent on the thickness of each printer unit, an attempt has been made to shorten the dot distance by rendering each thickness thin. However, each printer unit inevitably becomes weak in mechanical strength as a result of such an attempt.
Alternatively, each of the printing wires has been bent or deformed to narrow a distance between two adjacent ones of the printing wires. In this event, the printing wires become long and heavy. Accordingly, an impact printer head becomes large and bulky. It is difficult with the impact printer head to drive each printing wire at a high speed. Undesired tension or stress might be imposed on each bent printing wire when the bent printing wires are slidably supported by a guide or guides.